Rollup merge of rust-lang#116161 - Soveu:varargs2, r=cjgillot

Stabilize `extended_varargs_abi_support`

I think that is everything? If there is any documentation regarding `extern` and/or varargs to correct, let me know, some quick greps suggest that there might be none.

Tracking issue: rust-lang#100189

Author: jieyouxu

std/src/lib.rs

@@ -290,7 +290,6 @@
 #![feature(doc_masked)]
 #![feature(doc_notable_trait)]
 #![feature(dropck_eyepatch)]
-#![feature(extended_varargs_abi_support)]
 #![feature(f128)]
 #![feature(f16)]
 #![feature(if_let_guard)]